Refrigeration systems with centrifugal compressors and air cooled condensers



Jan. 9, 1968 J. R. HARNISH REFRIGERATION SYSTEMS WITH CENTRIFUGAL COMPRESSORS AND AIR COOLED CONDENSERS Filed June 20, 1966 THERMOSTAT TI OUTDOOR EVAPTATOR 3 THERMOSTAT B 2|,22 OUT :1 2o 29 B2 28 c MOTOR f J 2s 7 P 25 EV F HTS LTS AIR COOLED CENTRIFUGAL CONDENSER THERMQSTAT T2 GOMPRESSOR PRESSURESTAT P IS L R28 RETURN 42 F|G.5

l s2- HTS 2 LTS 39 22 FIG.6. -a|

82!) b 0PE N VANES 28 PISTON movsmsm CLOSED VANES mm H 9 u FIG.4. 2| 2% zs yw zs HTS LTS HTS LTS ms 24 INVENTOR= JAMES R.,HARN|SH, W W

ATTORNEY United States Patent REFRIGERATION SYSTEMS WITH CENTRIF- UGAL COMPRESSORS AND AIR COOLED CONDENSERS James R. Hamish, Stannton, Va., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed June 20, 1966, Ser. No. 558,880 8 Claims. (Cl. 62201) This invention relates to refrigeration systems using centrifugal compressors, and air-cooled condensers.

Presently used refrigeration systems with centrifugal compressors use, due to the operating characteristics of centrifugal compressors, water-cooled condensers. Due to water shortages in many locations, it is desirable to be able to use air-cooled condensers with such compressors.

A centrifugal refrigerant compressor must be designed to have sufiicient impeller tip speed to provide adequate pumping head to meet the lowest expected suction pressure coincident with the highest expected discharge pressure. Should the system head requirement exceed the available compressor head, the compressor will surge, with discharge gas periodically surging to the suction side. When this happens, the compressor stops pumping, noise is excessive, and the equipment may be damaged. This condition occurs at relatively high outdoor ambient temperatures when condensers cooled by outdoor air are used. Should the compressor speed be increased when this condition occurs, it would be extremely ineflicient at any other condition, and its operating range would be reduced.

This invention provides a control for resetting the thermostat which controls such a system so that at high outdoor temperatures, the load on the compressor is reduced. By reducing the compressor capacity, the evaporator and condenser temperature splits become smaller so that the system head requirement is reduced. Furthermore, the head capability of the compressor may actually increase above the design point at partially unloaded conditions. Reducing the compressor capacity will reduce the cooling provided by the system but this should be acceptable considering the advantages gained.

An object of this invention is to prevent surging of a centrifugal refrigerant compressor in a refrigeration system using a condenser cooled by outdoor air.

Another object of this invention is to decrease the load on a centrifugal refrigerant compressor in a refrigeration system using a condenser cooled by outdoor air, during high outdoor temperatures.

This invention will now be described with reference to the annexed drawings, of which:

FIG. 1 is a diagrammatic View of a refrigeration system embodying this invention;

FIG. 2 is an enlarged fragmentary view of the system used for adjusting the spin vanes in the refrigerant inlet of the compressor of FIG. 1;

FIGS. 3a and 3b are diagrammatic views of control relays used;

FIG. 4 is a simplified circuit schematic of the electrical control system used;

FIG. 5 is a fragmentary diagrammatic view of a control which can be used instead of the one shown by FIG. 1 to reset the load responsive thermostat, and

FIG. 6 is a fragmentary diagrammatic view of another control which can be used instead of the one shown by FIG. 1, to reset the load responsive thermostat.

Referring first to FIG. 1 of the drawings, a centrifugal refrigerant compressor C, driven by an electric motor CM, has its refrigerant outlet connected by discharge gas tube 10170 an air-cooled condenser 11. The tube 10 may contain a pressurestat P. The condenser 11 is connected by liquid tube 12, expansion valve EV and tube 13 to an evaporator 14 which is of the shell-and-tube type. The liquid tube 12 may contain a thermostat T2. The evaporator 14 is connected by suction gas tube 15 to the axial, refrigerant inlet of the compressor C. The evaporator 14 has a water inlet tube 16, and a water outlet tube 17 for connection to local air cooling units which are not shown. A thermostat T1 connected in the tube 17, is connected by tube 20 to bellows B1 which is connected by rod 21 to switch arm 22 between the ends of the latter.

The switch arm 22 is pivoted at one end to fixed support 23, and has a switch contact 24 on its other end. A fixed contact 25 is at one side of the contact 24, and another fixed contact 26 is at the opposite side of the contact 24. The contacts 24 and 25 form a switch LTS at the low end of a deadband, and the contacts 24 and 26 form a switch HTS at the upper end of the deadband. An outdoor air thermostat ODT is connected by tube 28 to bellows B2 which is connected by rod 29 to the switch arm 22 opposite where the rod 21 is connected. A fan F, driven by an electric motor FM, moves outdoor air over the surface of the condenser 11.

Referring now to FIG. 2 of the drawings, the compressor C, a fragment of which is shown by FIG. 2, and which is disclosed in detail in Patent No. 3,251,539 of R. W. Wolfe and R. R. Young, has an axial inlet passage 30 containing spin vanes 31 which have supporting and adjusting rods 32 journalled for rotation in wall 33 of the compressor C. The vanes 31 have off-center pins 34 extending into an annular slot 35 in annular piston 36. The piston 36 has outer portions in slidable contact with surfaces of compressor wall 37, and has inner portions in slidable contact with surfaces of the wall 33. The right end portion of the piston 36 has an enlargement 39 with a cylinder passage portion 40 formed by portions of the walls 33 and 37 to the right of its right end. A cylinder passage 41 is formed within the wall 37 to the left of the enlargement 39. A fluid return and supply tube 43 connects with the passage 40, and a fluid supply and return tube 44 connects with the passage 41.

A three-way valve VA, adjustable by a solenoid SA is connected to the tube 44, and a three-way valve VB, adjustable by a solenoid SE is connected to the tube 43. A conventional source of fluid under pressure which is not shown, and which may be an oil pump driven with the compressor C, is connected through tube 46 and checkvalve 48 to the valve VA, and is connected through the tube 46, check-valve 51 and tube 50 to the valve VB. The valves VA and VB are connected to the fluid return tube 42. When the solenoids SA andSB are energized, they adjust the valves VA and VB respectively, to permit flow through the tube 44 into the cylinder passage 41, and to permit flow from the cylinder passage 40 through the tube 43. When the solenoids SA and SB are deenergized, they adjust the valves VA and VB respectively, to permit flow through the tube 43 into the cylinder passage 41), and to permit fluid flow from the cylinder passage 41 through the tube 44.

Referring now to FIGS. 3a and 3b of the drawings, a relay R1 has a-normally closed switch R18, and another relay R2 has a normally open switch R28.

Referring now to FIG. 4, the relay R1 is connected in series with the switch HTS to electric supply lines L1 and L2. The relay R2 is connected in series with the switch LTS to the lines L1 and L2. The solenoid SA is connected in series with the switch R18 to the lines L1 and L2. The solenoid SE is connected in series with the switch R28 to the lines L1 and L2.

Referring now to FIG. 5 of the drawings, the thermo-= aasz, 185

stat T2 in the liquid tube 12 is connected by tube 28a to bellows 132a which is connected by rod 2% to the switch arm 22. When the thermostat T2 is used, the thermostat ODT is not used.

Referring now to FIG. 6 of the drawings, the pressurestat P in the discharge gas tube 10 is connected by tube 28b to bellows B212 which is connected by rod 2% to the switch arm 22. When the pressurestat P is used, the thermostats ODT and T2 are not used.

Operation Referring first to FIGS. 14 of the drawings, discharge gas from the compressor C is supplied through the tube 10 into the condenser 11. Refrigerant liquid flows from the condenser 11 through the tube 12, the expansion valve EV and the tube 13 into the evaporator 14 where the refrigerant is evaporated and chills the water recirculated through the evaporator. Gas flows from the evaporator 14 through the suction gas tube 15 into the inlet passage of the compressor C, and past the spin vanes 31 into the impeller which is not shown, of the compressor. Since the solenoid SA is normally energized as shown by FIG. 4, the valve VA is normally adjusted to pass compressed fluid through the tube 44 into the cylinder passage 41 against the piston projection 39, thus tending to force the piston 36 to the right so as to rotate the spin vanes 31 towards open position. But, since the solenoid SE is normally deenergized as shown by FIG. 3, the valve VB is adjusted to pass compressed fluid through the tube 43 into the cylinder passage 40, preventing movement of the piston so that it and the spin vanes 31 are in hold positions.

When the cooling load is such that the thermostat T1 calls for additional cooling, it closes the switch LTS, and energizes the relay R2 which closes its switch R28, energizing the solenoid SB which adjusts the valve VB to flow fluid from the cylinder passage 40 through the tube 43 into the fluid return tube 42. The piston 36 is moved to the right by the compressed fluid supplied by the valve VA into the cylinder passage 41, and rotates the spin vanes 31 towards open positions for increasing the output of the compressor C. When the temperature of the water flowing through the tube 17 decreases to the operating point of the thermostat T1, the latter opens the switch LTS which deenergizes the relay R2 which opens its switch RZS, deenergizing the solenoid SB which adjusts the valve VB to supply compressed fluid into the cylinder passage 40 to stop movement of the piston 36 and of the spin vanes 31, placing them in hold positions.

When the cooling load decreases, the thermostat T1 closes its switch HTS which energizes the relay R1 which opens its switch R1S, deenergizing the solenoid SA. The switch LTS is open at this time, and deenergizes the relay R2 which opens its switch R28, deenergizing the solenoid SB. As previously explained, the valves VA and VB are now adjusted to permit compressed fluid flow into the cylinder passage 40, and to permit fluid flow from the cylinder passage 41 into the return tube 42. The piston 36 moves to the left, and rotates the spin vanes 31 towards closed positions, reducing the output of the compressor. When the temperature of the water flowing through the tube 17 increases to the operating point of the thermostat T1, it opens the switch HTS, and deenergizes the relay R1 which closes its switch RlS which reenergizes the solenoid SA. The latter adjusts the valve VA to permit compressed fluid to flow into the cylinder passage 41, stopping movement of the piston 36 and of the vanes 31, placing them in hold positions.

The operation described in the foregoing is normal operation when the outdoor temperature is too low for the outdoor air thermostat ODT to have reset the thermostat T1. By way of example, the system may be designed to maintain a chilled water temperature of 45 F., with an evaporator temperature of 37 F., and a condensing temperature of 120 F., when the outdoor temperature is 4 not above F. If the outdoor temperature should increase to 103 F., the outdoor thermostat ODT would reset the thermostat T1 to maintain a chilled water temperature of about 50 F. It does this by exerting force through the bellows B2 to oppose the force acting on the switch arm 22 through the bellows B-l from the thermostat T 1, so that a higher than design temperature of the water flowing through the tube 17 is required to provide suflicient force to close the switch LTS. The evaporator temperature would be about 43 F., and the condensing temperature would be about 128 P. so that the compressor would operate without surging. While the cooled space temperature would increase above its design level, such a slight increase should be acceptable considering the very high outdoor temperature, and the benefit gained.

In the operation of FIG. 1 modified as shown by FIG. 5, the outdoor thermostat ODT is not used, but the thermostat T2 in the liquid tube 12 is used. The increased outdoor temperature would cause the condensing temperature to increase conformably, so that the thermostat T2 can be used to reset the thermostat T1 in the manner that the thermostat ODT resets it.

In the operation of FIG. 1 as modified by FIG. 6, the outdoor thermostat ODT is not used; the thermostat T2 is not used, but the pressurestat P in the discharge gas tube 10 is used. The increased outdoor temperature would cause the discharge gas temperature to increase conformably, so that the pressurestat P can be used to reset the thermostat T1 in the manner that the thermostat ODT resets it.

What is claimed is:

1. In a refrigeration system comprising a centrifugal refrigerant compressor, a condenser, an expansion means, and a fluid chilling evaporator connected in series in the order named in a refrigeration circuit; means for flowing outdoor air over the surface of said condenser; means for adjusting the output of said compressor; and means including thermostatic means responsive to the temperature of the fluid chilled by said evaporator for adjusting said output varying means to increase the output of said compressor on a predetermined increase in the temperature of said fluid; the improvement comprising means including means responsive to a condition caused by a predetermined increase in outdoor temperature, connected to said thermostatic means, for resetting said thermostatic means so that it does not adjust said output varying means to increase the output of said compressor until there is a fluid temperature higher than said first mentioned increase in fluid temperature.

2. The invention claimed in claim 1 in which said means responsive to a condition caused by a predetermined increase in outdoor temperature comprises an outdoor air thermostat.

3. The invention claimed in claim 1 in which said means responsive to a condition caused by a predetermined increase in outdoor temperature comprises a thermostat connected in said circuit between said condenser and said expansion means.

4. The invention claimed in claim 1 in which said means responsive to a condition caused by a predetermined increase in outdoor temperature comprises a pressurestat connected in said circuit between said compressor and said expansion means.

5. In a refrigeration system comprising a centrifugal refrigerant compressor, a condenser, an expansion means, and a fluid chilling evaporator connected in series in the order named in a refrigeration circuit; means for flowing outdoor air over the surface of said condenser; said compressor having an axial inlet passage, having spin inducing vanes in said passage, having means for rotating said vanes towards open or closed positions, and having means including thermostatic means responsive to the temperature of the fluid chilled by said evaporator for causing said rotating means to rotate said vanes towards open positions on a predetermined increase in the temperature of said fluid; the improvement comprising means including means responsive to a condition caused by a predetermined increase in outdoor temperature, connected to said thermostatic means, for resetting said thermostatic means so that it does not cause said rotating means to rotate said vanes towards open positions until there is a fluid temperature higher than said first mentioned increase in fluid temperature.

6. The invention claimed in claim 5 in which said means responsive to a condition caused by a predetermined increase in outdoor temperature comprises an outdoor air thermostat.

7. The invention claimed in claim 5 in which said means responsive to a condition caused by a predetermined increase in outdoor temperature comprises a thermostat responsive to the temperature of the refrigerant flowing in said circuit between said condenser and said expansion means.

8. The invention claimed in claim 5 in which said means responsive to a condition caused by a predetermined increase in outdoor temperature comprises a pressurestat responsive to the pressure of the refrigerant flowing in said circuit between said compressor and said expansion means.

References Cited UNITED STATES PATENTS 3,248,896 5/1966 Plaster 62227 XR 1 MEYER PERLIN, Primary Examiner. 

1. IN A REFRIGERATION SYSTEM COMPRISING A CENTRIFUGAL REFRIGERANT COMPRESSOR, A CONDENSER, AN EXPANSION MEANS, AND A FLUID CHILLING EVAPORATOR CONNECTED IN SERIES IN THE ORDER NAMED IN A REFRIGERATION CIRCUIT; MEANS FOR FLOWING OUTDOOR AIR OVER THE SURFACE OF SAID CONDENSER; MEANS FOR ADJUSTING THE OUTPUT OF SAID COMPRESSOR; AND MEANS INCLUDING THERMOSTATIC MEANS RESPONSIVE TO THE TEMPERATURE OF THE FLUID BY SAID EVAPORATOR FOR ADJUSTING SAID OUTPUT VARYING MEANS TO INCREASE THE OUTPUT OF SAID COMPRESSOR ON A PREDETERMINED INCREASE IN THE TEMPERATURE OF SAID FLUID; THE IMPROVEMENT COMPRISING MEANS INCLUDING MEANS RESPONSIVE TO A CONDITION CAUSED BY A PREDETER- 